Method of conducting electrolytic operations



April 21, 1925. 1,534,709 F. A. HOLT METHOD OF CONDUCTING ELECTROLYTIC OPERATIONS Filed May 1'7 1924 Patented Apr. 21, 1925.

T OFFICE.

FRANCIS A. HOL'I,l OF ELMHUBST, NEW YORK.

METHOD 0F (lON'IDUt'YllING ELECTROLYTIC OPERATIONS.

Application led lay 17, 1924. Serial No. 714,079.

To all whom t may concern:

Be it known that I, FRANCIS A. I-IoL'r, a citizen of the United States, residing at Elmhurst, in the county of Queens and State of New York, have invented certain new and useful Improvements in Methods of Conducting Electrolytic O erations, of which the following. is a speci cation.

This invention relates to electrolytic processes and particularly to improvements in methods of depolarizing the electrodes used therein. The invention is based upon the periodic reversal of the electrolyzing current, and comprises as essential features the regulation of the interval between reversals, and of the duration of the reversed current, in accordance with the requirements of the particular operation involved.

In many electrolytic processes polarization is a serious obstacle. The most common manifestation of this effect is the formation of a gaseous iilm upon the electrodes. Such films have high electrical resistance and may develop an objectionable counter electromotive force. They may also injure t-he product, as is generally the case when a hydrogen iilm forms upon the cathode in the electroplating of copper and other metals.

Numerous mechanical methods have been proposed for counteracting the adverse effects of polarization. For example, air or other g-as has been forced about the electrodes, the bath jhas been agitated, or the electrodes momentarily lifted from the bath, to dislodge the adherent gas bubbles or per- 'mit them to escape. Such methods are often inecient and usually inconvenient, if not impractical in commercial operation. y,

It is well known that if the electrolyzing current be reversed, the polarizing film will be dissipated, and lseveral methods' based upon this principle have been suggested. The mechanical elect of dislodging gas bubbles by periodic reversal of the current has been taken advantage of in the electrolytic pickling or scrubbing of sheet metal. Also, a transformer has been so connected in thecircuit that when the current from the battery or generator is reduced or interrupted by formation of a polarizing film, aninduced Acurrent of relatively high voltage will pass in the reverse direction. This method maintains a rather constant battery current, but it does not permit re ulation ofthe current reversal withthe a vantages referred to hereinafter.'

A method analogous to that just described is the use of a direct current upon which an alternating current is su erposed. This procedure is relatively inegicient and the rapidity of alternation of all commercially available A.. C. currents makes it impractical to` obtain the best results.

Inaccordance with thev present invention, the electrolyzing current is passed until the polarization begins tov be detrimental, and is then reversed for a eriod just sufficient to restore the system substantially to its initial electrical condition. In applying the invention to particular operations it is necessary to determine the optimum periods for reversal and for the duration of the reversed current. Observation and experiment will give the desired information. The resent invention is applicable to ayvide var1ety of processes Vand it is obviously impracticable to give precise details for all. The followin example, which is illustrative of one appllcation of the invention, will suffice to show the principles involved.

In the art of electroplating with copper it has long been known that if currents of high density are used the deposited metal is liable to be spongy, dark, and poorly adherent. It appears that such burnt deposits are frequent-ly caused by Simultaneous deposition of metal and hydrogen upon the cathode. Up to the point where this effect begins, the density and adherence of the deposited metal increase with the increase of the current density.

I have discovered that the advantageous effects of high current densityV may be obtained in an enhanced degree, and without polarization diiiculties, if the current is passed at well above the normally permissible rate, for a short period, and their momentarily reversed. Thus in depositing copper from an acidiied copper sulfate solution, I may pass a current from three to four times the normal rate for about ten seconds and then reverse the current for about onetenth second only. Thiscycle of alterna- .but

tions can be kept up as long as desired and a bright deposit of high quality will be obtained.

In the accompanying drawing, illustrating one embodiment of the invention,

Fig. l is a Wiring diagram of an installation for electroplating or analogous purposes; and

Fig. 2 is a side elevation of a similar 1nstallation. v I

Reference numeral 1 denotes an electrolytic bath having electrodes 2 and 3 connected by conductors 4 and 5 with current reversing means 6. This means as shown is a reversing colnmutator of standard type, various other equivalent devices are known'in the art and may be used. The period of reversal of the commutator may be regulated by properly proportioning lts conductor segments` in the usual manner. Current is supplied through conductors 7 and 8. connected to a Suitable D. C. supply.

In Fig. 2 a motor 9 is shown as connected through reduction gearing 10 to the commutator 6. The commutator may of course be rotated by other suitable means, or manually, if desired.

An especially important feature of the regulated reversal of the current in accord-i ance with the present invention, is the speeding upfof the process which results from the high current rate which it permits. It will be noted, further, that there is only a small Wastage of current in the short reversed phase and that this is much more than compensated for bythe substantially reduced depolarizing resistance .and counter electromotive force'. t

The inventioir'may be applied also to various other purposes, as in the electrolytic production of materials in aqueous or other liquid baths, or in fused baths. A further application is in the forming or subsequent charging of storage battery plates.

As distinguished from prior methods, the present invention provides for the accurate regulation of the period and duration of about the optimum rate until 'polarization begins to be detrimental, reversing the current only until the polarizing eect is substantially removed, and continuing `this cycle of operations until electrolysis has taken place to the desired extent.

2.n In an electrolytic operation, the method which comprises passing a direct electrolyzing current through the electrolytic bath at a rate substantially in excess of that which normally would lead to detrimental polarization, and reversing the current Whenever necessary to counteract the effect of polarization, whereby a currentl of relatively high density may be Aused with advantage.

3. An electroplating method comprising passing a direct electrolyzing current through an electrolytic bath, reversing the current for a brief period at regulated intervals to prevent formation of a polarizing deposit, and continuing the cycle of reversals until the desired thickness of deposited metal is obtained.'

4. A method of electroplating copper from an acidiiied solution of a suitable copper salt, comprising passing a direct electrolyzing current of relatively high density through the solution, whereby a dense, adherent deposit is formed at a rapid rate, and periodically reversing the current when necessary to dissipate the polarizing film Which tends to form upon the cathode.

5. Method according to cla-im 4, in which the direct electrolyzing current is passed for about ten seconds and the reverse current for about one-tenth second.

In testimony whereof, I aiiix my signature.

FRANCIS A. HOLT. 

